Thin-walled carbonaceous honeycomb structures and process for making same

ABSTRACT

A THIN-WALLED CARBONACEOUS HONEYCOMB STRUCTURE HAVING A LARGE SURFACE TO WEIGHT RATIO AND CONSISTING OF THIN-WALLED CARBONACEOUS CELLS; AND A PROCESS FOR MAKING THE SAME. THE PROCESS INCLUDES COATING ELONGATED TUBE OR ROD ELEMENTS WITH A COATING MATERIAL CAPABLE OF BEING CARBONIZED, ARRANGING THE ELONGATED ELEMENTS SO THAT THEY CONTACTT ONE ANOTHER TO FORM A HONEYCOMB-LIKE BLOCK, DRYING THE COATED ELEMENTS SO ARRANGED, REMOVING THE ELONGATED ELEMENT SUBSTTRATES FROM THE DRIED HONEYCOMBLIKE BLOCK IF THE SUBSTRATES, THEMSELVES, ARE NOT CAPABLE OF BEING CARBONIZED, AND FIRING SAID HONEYCOMB-LIKE BLOCK TO ACHIEVE THE CARBONACEOUS PRODUCT.

y 1974 TAKAYUKR YQSHRKAWA E AL 3,825,460

THIN-WALLED CARBONACEOUS HONEYCOMB STRUCTURES AND PROCESS FQR MAKINGSAME Filed Dec. 29, 1971 United States Patent 3,825,460 THIN-WALLEDCARBONACEOUS HONEYCOMB STRUCTURES AND PROCESS FOR MAKING SAME TakaynkiYoshikawa and Eiiehi Hisada, Nagoya, and Tooru Hujii, Yokkaichi, Japan,assignors to Nippon Toki Kabnshiki Kaisha (Noritake 'Co., Ltd.),Nagoyashi, Japan Filed Dec. 29, 1971, Ser. No. 213,425 Claims priority,application Japan, May 18, 1971, 46/33,519 Int. Cl. B29c 25/00; 1332b1/08 U.S. Cl. 156-296 Claims ABSTRACT OF THE DISCLOSURE A thin-walledcarbonaceous honeycomb structure having a large surface to weight ratioand consisting of thin-walled carbonaceous cells; and a process formaking the same. The process includes coating elongated tube or rodelements with a coating material capable of being carbonized, arrangingthe elongated elements so that they contact one another to form ahoneycomb-like block, drying the coated elements so arranged, removingthe elongated element substrates from the dried honeycomblike block ifthe substrates, themselves, are not capable of being carbonized, andfiring said honeycomb-like block to achieve the carbonaceous product.

This invention relates to carbonaceous honeycomb structures made up ofthin-walled cells with a large surface-to-weight ratio and to a processfor forming the same.

According to this invention, there can be manufactured even extremelythin-walled, carbonaceous honeycomb structures with a large surface toweight ratio and there can further be produced honeycomb structuresconsisting of honeycomb cells which have any size and shape and are madeof any carbonaceous material, depending on the use of the honeycombstructures. In addition, these honeycomb structures can easily bemanufactured by the process of this invention.

The honeycomb structures which are publicly known are, for example,metal-made ones such as aluminummade ones which are light in weight andiron-made ones which are excellent in structural strength, syntheticresinmade ones and ceramics-made ones. Although these conventionalstructures are different in use depending on the kind of material fromwhich they are made, they have heretofore been used as a light-weightreinforcing structural material, heat exchanger, catalyst carrier,catalyst support, packing material or the like.

The novel carbonaceous honeycomb structures prepared according to thisinvention may also be effectively used as a light-weight refractoryreinforcing element, heat exchanger, catalyst or catalyst carrier, oradsorbent material. They contain many parallel cells through the bodyfrom one surface to the opposite one. The term cell used herein means anarrow hollow body having a thin wall and a specific shape incross-section. To form a honeycomb structure, such cells are bound intoa bundle wherein they are bonded with one another.

In the accompanying drawing, FIG. 1 is a perspective view of acarbonaceous honeycomb structure of this invention consisting ofhoneycomb cells which are circular in cross-section;

FIG. 2 is a perspective view of a carbonaceous honeycomb structure ofthis invention consisting of cells which are triangular incross-section;

FIG. 3 is a perspective view of a carbonaceous honeycomb structurewherein the longitudinal axes of the honeycomb cells arenon-perpendicular to two parallel planar surfaces of the structure;

FIG. 4 is a perspective view of a carbonaceous honeycomb structureconsisting of cell groups which are different in size of cellcross-section; and

FIG. 5 is a perspective view of a carbonaceous honeycomb structureconsisting of cells which are hexagonal in cross-section and have atwo-layer wall.

Referring now to the accompanying drawing, the honeycomb structures ofthis invention will be detailed below. According to this invention,there can be produced various carbonaceous thin-walled honeycombstructures consisting of honeycomb cells which may be circular,elliptical, triangular, polygonal or the like in cross-section as seenfrom FIGS. 1 to 5 and which may have a cell size 1 of as small as 1.0mm. and a wall 2 of as thin as 0.1 mm. As shown in FIG. 4, it is alsopossible to obtain a honeycomb structure wherein two or more groups ofdifferently sized and/or shaped cells are symmetrically orasymmetrically arranged.

The terms cell shape and cell size used herein mean the cross-sectionalshape of a cell and the inner diameter of a cell if its cell shape iscircular (or the distance between the opposing inner sides if polygonalwith even-numbered sides, or approximately the distance between one ofthe apexes and the side opposing to the apex if triangular or polygonalwith odd-numbered sides), respectively.

The process of this invention is summarized as follows.

Rods or cylinders the cross-sectional size and shape-of which are thesame as those of the cells being manufactured, are immersed in a slurryof carbon or organic carbonizable powder and an organic binder in asuitable solvent, withdrawn from the slurry and then centrifugalized toremove an excess of the slurry attached thereto leaving the requiredamount of the slurry thereon. Prior to drying of the slurry coated, thethus-coated rods or cylinders are arranged so that they contact witheach other to form a green honeycomb block. The green block is thendried. The dried green block is fired by heating to a temperature atwhich the rod or cylinder substrates are carbonized, in a non-oxidizingatmosphere such as a nitrogen stream to obtain a honeycomb structure ifthe substrates are those which are prefectly carbonized during firing,whereas it is fired as mentioned above after removing the substrates outof the green block to obtain a honeycomb structure if they are thosewhich are not completely carbonized during firing. The carbonizingtemperature and time vary with the components of the slurry. Dependingupon their uses, the once carbonized products may be impregnated with anatural or synthetic resin which may then be carbonized or they may betreated for activation to increase their specific surface area, that is,surface to weight ratio.

A coating material for use in covering the rod or cylinder substrates iscomposed essentially of a powdered carbon or a powdered organic materialwhich is capable of being carbonized when fired and of an organic bindertherefor. Before coated, the coating material is dissolved, suspended oremulsified in a suitable solvent to form a slurry thereof.

As mentioned above, this invention is directed to a thin-walled,carbonaceous structure with a large surfaceto-weight ratio and to aprocess for manufacturing the same.

Honeycomb structures, in general, are extremely large in surface toweight ratio and superior in mechanical strength. Because of this, theyare very useful as, for example, catalysts or catalyst carriers whichare frequently used in the chemical industry. They are advantageouslyused in a reaction system wherein reactants react with each other whileflowing in gaseous or liquid phase, due

to their extremely small resistance to the flow of the reactants.

As is well known, carbon varies in crystal form from amorphous carbonthrough graphite to diamond. There has recently been produced a new formof carbon such as Glassy Carbon (the trademark of Tokai Electrode Co.,Ltd., Japan) in some countries.

The carbonaceous materials of which the honeycomb structures of thisinvention are composed, may be carbon in each of said crystal forms orin said Glassy Carbon form. By the process of this invention thestarting carbonaceous materials from which the honeycomb structures ofthis invention will be made, can be changed in degree of crystallizationdepending on the use of the structures and can be locally differentlychanged in degree of crystallization. For example, if the structuresbeing produced are intended to be used as a catalyst or catalyst carrierin chemical processes, they will be required to be high in chemicalactivity. In this case the surface of the structures or the wholethereof should be activated to be made active carbon.

If the structures being produced are intended to be used as a refractoryreinforcing element which requires mechanical strength, they will bemade a dense graphite in quality or crystal form.

The structure "of the honeycomb structures varies not only with saidquality or crystal form of the carbonaceous material from which thehoneycomb cells are made but with the shape, size and arrangement of thecells. The cells may be made, for instance, circular, elliptical,triangular or polygonal in cross-sectional shape. They may also be madeso that they have a desired cell size, shape and/or length. The cellsize is preferably 1.0-10.0 mm. according to this invention. The cellsmay further be made with a desired thickness which preferably rangesfrom 0.1 mm. to mm. The optimum thickness of the cells is determined incompliance with the size of cross-section, that is, cell size thereof.

The honeycomb structures of this invention may be composed of, incombination, two or more groups of cells which are dilferent in cellshape and size. For instance, there may be produced a honeycombstructure wherein cells of small cell size positioned centrally withrespect to the longitudinal axis of the structure are surrounded bythose of large cell size, as shown in FIG. 4.

As previously mentioned, the process of this invention comprises thesteps of coating rods or tubes with a slurry of a coating material whichis capable of being carbonized when fired in a non-oxidizing atmosphere,arranging the slurry-coated rods or tubes so that they contact oneanother as predetermined to form a green block or structure having apredetermined appearance, drying the green structure and, afterwithdrawing the rod or tube substrates from the dried green structure ifthey are not carbonizable when fired in a non-oxidizing atmosphere orwithout withdrawing them if they are carbonizable when fired in such anatmosphere, firing the dried green structure in a non-oxidizingatmosphere to obtain a honeycomb structure the body of which has beencarbonized.

Coating materials which may be carbonized by firing in a non-oxidizingatmosphere, include carbon powder such as carbon black, natural orartificial graphite powder, coke powder and coal powder; and organicmaterials such as sugar, powdered thermosetting synthetic resin (forexample, a phenol-formaldehyde resin in powder form), powdered coconutshell, powdered walnut shell and short-cut natural or artificial fibers.It is necessary, however, to incorporate the coating material with asuitable organic binder therefor since the former will provide greenmoldings having poor strength when coated and molded on the rod or tubesubstrates without the latter. Binders which may be used includephenol-formaldehyde resins, urea resins, expoxy resins and glue.Solvents which may be used in making a slurry of such coating materialand binder, are water, ethyl alcohol, methyl alcohol, ethyl methylketone, toluene and the like. The rods or tubes used to form a coatingor molding thereon will determine the shape and size of the cells of ahoneycomb structure to be obtained and they should therefore have ashape and size required to form the cells. For instance, round rods ortubes of approximately 2 mm. in outer diameter may be used tomanufacture a honeycomb structure composed of tubular cells of about 2mm. in inner diameter The rods or tubes which may be used, arequalitatively divided into three groups A, B and C. The group A includesrods or tubes which can be carbonized by firing in a non-oxidizingatmosphere. These rods or tubes may be made of paper or a thermosettingresin such as a phenol-formaldehyde resin prepared by polycondensation.The group B includes rods or tubes made of a metal such as aluminum oriron, which cannot be carbonized by firing in a non-oxidizingatmosphere. The group C includes rods or tubes made of a thermoplasticsynthetic resin such as polyvinyl chloride or polyethylene, which can beremoved by melting, dissolving in a solvent, or the like. The rods ortubes of the group A may be carbonized in situ when fired in anon-oxidizing atmosphere, those of the group B must be withdrawn beforefiring in a non-oxidizing atmosphere and those of the group C may bewithdrawn or dissolved in a solvent before firing or may be moltenduring firing in a non-oxidizing atmosphere.

The carbonization step according to this invention is as follows.

The green honeycomb block or structure may be fired in an atmospherewhich is made non-oxidizing by passing therethrough an inert gas such asnitrogen, helium, a gaseous mixture of hydrogen and nitrogen, an ammoniadecomposition gas (N -l-H carbonic acid gas or the mixtures thereof orit may be fired in carbonaceous powder, such as graphite or coal powder,within it is buried. The firing temperatures and times may widely varydepending on the required quality of honeycomb structures -to bemanufactured.

If the material composing a final honeycomb structure being obtained isrequired to be amorphous carbon, the firing temperature used should bein a relatively low range of from 400 to 500 C., while if such materialis required to be graphite the firing temperature used should be highenough for graphitization.

The carbonaceous material of an ordinary honeycomb structure maypartially be made activated carbon. For example, the activation may beeffected at about 1000 C. in an atmosphere wherein oxygen isincorporated in a small amount or may be effected in the presence ofsteam at about 1000 C.

If the honeycomb structures prepared according to this invention aredesired to be further increased in mechanical strength, they may befurther treated. The further treatment may be effected by, for example,impregnating the honeycomb structures with a resin, heating theresin-impregnated structures to cure the resin so impregnated and, ifrequired, again firing the thus-treated structures in a non-oxidizingatmosphere to carbonize the cured resin. The resins which may be usedinclude a phenol-formaldehyde resin. The resin may be dissolved inmethanol, etc, and used in the impregnation.

This invention will be illustrated by the following examples.

Example 1 Round metallic rods (2.5 mm. 1; x 300 mm. long) were wounddoubly with thin paper and vertically dipped so deep in a slurry of thefollowing composition that their lower end reached mm. below the surfaceof the slurry for three seconds to form a 1.0 mm. thick coating of theslurry on the part of the rods so dipped.

Composition of the slurry -Parts by weight Carbon black powder 7OPowdered phenol-formaldehyde resin 1 30 Methanol 50 1 Supplied under thetrademark of PR-217 N by Sumitomo Bakelite Co., Ltd., Japan.

Five hundred rods so coated were horizontally piled up so that theytogether formed a predetermined cube (60 mm. x 100* x 150 mm.), and thendried at room temperatures. The dried cube was separated from the rodsubstrates by slipping them out of the cube, to obtain a green honeycombstructure. The green structure was fired to a temperature of 1000 C. ata temperature-raising rate of 100 C./hour and then allowed to cool to aroom temperature to yield a carbonaceous honeycomb structure having anoverall size of 60 mm. x 100 mm. x 150 mm. and consisting of honeycombcells having a diameter of 2.3 mm. and wall of 0.2 mm. in thickness asshown in FIG. 1.

Example 2 Following the procedure of Example 1, the same metallic rodsas used in Example 1 were dipped in a slurry of the followingcomposition to be coated with the slurry.

Composition of the slurry Parts by weight Natural scaly graphite inpowder form 80 Liquid phenol-formaldehyde resin 1 20 Water 50 Suppliedunder the trademark of PR-94O by Sumitomo Five hundred rods so coatedwere horizontally piled so that they together formed a predeterminedcylindrical shape having a size of 85 mm. :1: x 150 mm., dried at a roomtemperature for 24 hours and further dried in a drying chamber at 110 C.for 8 hours to yield a green block. The green block was freed of the rodsubstrates by slipping them therefrom to obtain a green honeycombstructure which was then buried in natural scaly graphite powder filledin a refractory vessel, fired to a temperature of 1200 C. at atemperature-raising rate of 100 C./hour and allowed to cool to a roomtemperature thereby obtaining a cylindrical graphite honeycomb structurehaving an overall size of 80 mm. x 150 mm. and consisting of honeycombcells having a diameter of 2.3 mm. and a wall of 0.3 mm. in thickness.

Example 3 Paper-made tubes having a 3-mm. diameter and a 200-mm. lengthwere immersed in a slurry of the following composition to form anapproximately 2 mm. thick coating of carbonaceous material on thepaper-made tubes.

Composition of the slurry Parts by weight Walnut shell powder of 100 1or finer in particle size 90 Tar pitch 10 Toluol 50 Example 4Composition of the slurry Parts by weight a-cellulose fibers (inshort-cut form) 40 Cured, phenol-formaldehyde resin (in powder form)Vinyl acetate 20 Water 130 The rods so coated were piled to form apredetermined block of a size of 160 mm. x 110 mm. x 110 mm. which wasdried at a room temperature until the coatings decreased to 30% inmoisture content and then dried in a drier at C. for 15 hours. The blockthus dried was freed of the rod substrates by pulling them out thereofto obtain a green honeycomb structure which was then fired at atemperature-raising rate of 50 C./hr. to 1000 C. and thereafter allowedto cool to a room temperature thereby yielding a honeycomb structure of150 mm. x mm. x 100 mm. which was composed of amorphous carbon andconsisted of honeycomb cells with a hexagonal cross-section having sixsides of 3.8 mm. each.

Example 5 A green honeycomb structure prepared in the same manner as inExample 1 was fired at a temperature-raising rate of 100 C./hr. to 600C. in a nitrogen stream to produce a carbonized structure which was thenactivated at a temperature of 700-l000 C. in the presence of steamthereby obtaining a carbonaceous honeycomb structure wherein the carbonhas been activated. This structure had a specific surface area (asurface to weight ratio) of about 800 m. g.

Example 6 A green honeycomb structure prepared in the same manner as inExample 1 was fired at a temperature-raising rate of 100 C./hr. to atemperature of 1000 C. in a stream of nitrogen to produce a carbonizedstructure which was further treated with the following treating mixtureto form a coating of the mixture on the structure, fired at atemperature-raising rate of 100 C./hr. to 600 C. to carbonize thiscoating and then heated to 700-1000 C. in a stream of steam to activatethis carbonized coating only. The activated, carbonaceous honeycombstructure so obtained had a specific surface area of about 300 mP/g.

Composition of the treating mixture Parts by weight Powdered,phenol-formaldehyde resin 1 60 Methanol 40 1 Supplied under thetrademark of PR 217 N b S it Bakelite Co., Ltd., Japan. y um omo Example7 The graphite honeycomb structure prepared in Example 2 was buried ingraphite powder blended with silicon carbide powder and then allowed topass direct electric current vtherethrough to heat the structure toabout 1800 C. and consequently promote graphitization thereby obtaininga further graphitized honeycomb structure having an electric resistanceof of 0.010.

Example 8 The carbonaceous honeycomb structure prepared in Example 3 wastreated with the following treating mixture of the following compositionto form thereon a coating of the mixture, which coating was then curedto strengthen the structure.

Composition of the treating mixture Parts by weight Epoxy resin 70Curing agent Diluent Supplied under the trademark of Epikote 818 byShell Chemical 00., Ltd.

Supplied under the trademark of Eplcure Z by the same company.

Supplied under the trademark of Cardura E by the same company.

Example 9 The carbonaceous honeycomb structure prepared in Example 3 wastreated with the following treating mixture to form a coating thereof onthe structure and then fired at a temperature-rising rate of 100 C./hr.to 600 C. in a nitrogen stream to carbonize said coating.

Composition of the treating mixture Parts by weight Liquidphenol-formaldehyde resin 1 8O Methanol 20 Supplied under the trademarkof PR 940 by Sumitomo Bakelite Co., Ltd.

What we claim is:

l. A process for producing a thin-walled carbonaceous honeycombstructure which comprises (1) coating elongated tube or rod elementshaving a desired cross-sectional shape with a material capable of beingcarbonized when fired in a non-oxidizing atmosphere, said elongatedelements being made of a material capable of being car-bonized whenfired in a non-oxidizing atmosphere, (2) arranging the coated elongatedelements so that they contact one another and together form a desiredhoneycomblike block, (3) drying the coated elongated elements soarranged and then (4) firing the arranged coated elongated elements thusdried in a non-oxidizing .atmosphere to carbonize the elongated elementsubstrates and the coatings formed thereon thereby forming carbonaceouscells bonded with one another which constitute the thinwalledcarbonaceous honeycomb structure.

2. A process as claimed in claim 1, wherein the nonoxidizing atmosphereis one filled with carbon powder.

3. A process as claimed in claim 1 wherein said elongated elements aremade of paper.

4. A process as claimed in claim 1 wherein said elongated elements aremade of a thermosetting resin.

5. A process for producing a thin-walled carbonaceous honeycombstructure having a large surface-to-weight ratio which comprises 1)winding thin paper around metallic elongated tube or rod elements havinga desired cross-sectional shape, (2) coating the wound elongatedelements with a coating material composed essentially of -a powderedcarbonaceous material carbonizable when fired in a non-oxidizingatmosphere and of an organic binder therefor, (3) arranging the coatedelongated elements so that they contact one another and together form adesired honeycomb-like block, (4) drying the coated elongated elementsso arranged, (5) removing the elongated element substrates out of thedried coated material to obtain a honeycomb-like block free of saidelongated elements, and then (6) firing said honeycomb-like block in anon-oxidizing atmosphere to carbonize the block thereby producing thethin-walled carbonaceous honeycomb structure.

6. A process as claimed in claim 5, wherein the nonoxidizing atmosphereis one filled with carbon powder.

7. A process for producing a thin-walled carbonaceous honeycombstructure having a large surface-to-weight ratio which comprises (1)winding thin paper around thermoplastic elongated tube or rod elements,2) coating the wound elongated elements with a coating material composedessentially of a powdered carbonaceous material carbonizable when firedin a non-oxidizing atmosphere and of an organic binder therefore, (3)arranging the coated elongated elements so that they contact one anotherand together form a desired honeycomb-like bloc-k, (4) drying the coatedelongated elements so arranged, (5) removing the elongated elementsubstrates from the dried coated material to obtain a honeycomblikeblock free of said elongated elements, and then (6) firing saidhoneycomb-like block in a non-oxidizing atmosphere to carbonize theblock thereby producing the thin-walled carbonaceous honeycombstructure.

8. A process as claimed in claim 7 wherein said step of removing saidelongated elements includes longitudinally withdrawing said elongatedelements from said dried coated material. I

9. A process as claimed in claim 7 wherein said step of removing saidelongated elements includes dissolving said elongated elements with asolvent.

10. A process as claimed in claim 7 wherein said step of removing saidelongated elements includes heating said elongated elements to melt thelatter.

References Cited UNITED STATES PATENTS 2,369,006 2/1945 Banks 156-1973,632,385 1/1972 Schmitt et al. 16168 3,275,428 9/1966 Siegrnund 156-1973,667,984 6/1972 Adams 16168 2,749,254 6/1956 Slyh et al 11746 CC3,574,646 4/ 1971 Wismer et al 26429 GEORGE F. LESMES, Primary ExaminerP. J. T'HI BODEAU, Assistant Examiner U.S. Cl. X.R.

